Profiling
the heterogeneous landscape of cell types and biomolecules
is rapidly being adopted to address current imperative research questions.
Precision medicine seeks advancements in molecular spatial profiling
techniques with highly multiplexed imaging capabilities and subcellular
resolution, which remains an extremely complex task. Surface-enhanced
Raman spectroscopy (SERS) imaging offers promise through the utilization
of nanoparticle-based contrast agents that exhibit narrow spectral
features and molecular specificity. The current renaissance of gold
nanoparticle technology makes Raman scattering intensities competitive
with traditional fluorescence methods while offering the added benefit
of unsurpassed multiplexing capabilities. Here, we present an expanded
library of individually distinct SERS nanoparticles to arm researchers
and clinicians. Our nanoparticles consist of a ∼60 nm gold
core, a Raman reporter molecule, and a final inert silica coating.
Using density functional theory, we have selected Raman reporters
that meet the key criterion of high spectral uniqueness to facilitate
unmixing of up to 26 components in a single imaging pixel in vitro and in vivo. We also demonstrated
the utility of our SERS nanoparticles for targeting cultured cells
and profiling cancerous human tissue sections for highly multiplexed
optical imaging. This study showcases the far-reaching capabilities
of SERS-based Raman imaging in molecular profiling to improve personalized
medicine and overcome the major challenges of functional and structural
diversity in proteomic imaging.
Multiplexing capabilities and sensitivity of surface-enhanced Raman spectroscopy (SERS) nanoparticles (NPs) are strongly dependent on the selected Raman reporter. These Raman-active molecules are responsible for giving each batch of SERS NPs its unique spectral fingerprint. Herein, we studied four types of SERS NPs, namely, AuNPs labeled with trans-1,2-bis(4-pyridyl)ethylene (BPE), 4,4′-bis(mercaptomethyl)biphenyl (BMMBP), 5-(4pyridyl)-1,3,4-oxadiazole-2-thiol (PODT), and 5-(4-pyridyl)-1H-1,2,4-triazole-3-thiol (PTT), and demonstrated that the best level of theory could be chosen based on inner products of DFT-calculated and experimental Raman spectra. We also calculated the theoretical spectra of these Raman reporters bound to Au 20 clusters to interrogate how SERS enhancement would affect their spectral fingerprint. Importantly, we found a correlation between B3LYP-D3 calculated and experimental enhancement factors, which opens up an avenue toward predicting which Raman reporters could offer improved sensitivity. We observed 0.5 and 3 fM limits of detection for BMMBP-and PTT-labeled 60 nm AuNPs, respectively.
Modern
genomic sequencing efforts are identifying potential diagnostic
and therapeutic targets more rapidly than existing methods can generate
the peptide- and protein-based ligands required to study them. To
address this problem, we have developed a microfluidic enrichment
device (MFED) enabling kinetic off-rate selection without the use
of exogenous competitor. We tuned the conditions of the device (bed
volume, flow rate, immobilized target) such that modest, readily achievable
changes in flow rates favor formation or dissociation of target–ligand
complexes based on affinity. Simple kinetic equations can be used
to describe the behavior of ligand binding in the MFED and the kinetic
rate constants observed agree with independent measurements. We demonstrate
the utility of the MFED by showing a 4-fold improvement in enrichment
compared to standard selection. The MFED described here provides a
route to simultaneously bias pools toward high-affinity ligands while
reducing the demand for target-protein to less than a nanomole per
selection.
Assays for chemical biomarkers are a vital component in the ecosystem of noninvasive disease state assessment, many of which rely on quantification by colorimetric reactions or spectrophotometry. While modern advances in microfluidic technology have enabled such classes of devices to be employed in medical applications, the challenge has persisted in adapting the necessary tooling and equipment to integrate spectrophotometry into a microfluidic workflow. Spectrophotometric measurements are common in biomarker assays because of straightforward acquisition, ease of developing the assay's mechanism of action, and ease of tuning sensitivity. In this work, 3D-printed, discrete microfluidic elements are leveraged to develop a model system for assaying hyaluronidase, a urinary biomarker of bladder cancer, via absorbance spectrometry of gold nanoparticle aggregation. Compared to laboratory microtiter plate-based techniques, the system demonstrates equivalent performance while remaining competitive in terms of resource and operation requirements and cost.
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